The present invention relates to a conveyor with a metal detecting device for detecting of metal parts in a product to be conveyed, in particular in a crop.
More particularly, it relates to a conveyor with a metal detecting device, which has a magnet arrangement for producing a measuring magnetic field, through which the product to be conveyed is moved, with a sensor arrangement which registers a change in the measuring magnetic field and a signal evaluating device, which evaluates a signal outputted in case of a magnetic field change by the sensing device for recognizing a metal part in a product to be conveyed. Moreover, the present invention relates to a harvester which has such a conveyor, as well as to a corresponding method for detecting metal parts in a product to be conveyed.
Conveyors of the above mentioned general type with metal detecting devices as a rule are used in harvesters, in particular in self-propelled harvesters, such as for example forage harvesters, to detect metal bodies which eventually are entrained with the crop in the machine, for example a turning tine, a pasture fence post, a can, or a needle and to automatically turn off the machines in this case. Thereby a situation is prevented when the metal parts can cause damages in the machine or later can be taken during feeding the crop to the animals and can lead to injuries or death of animals.
In a typical construction such a conveyor is composed of one or several feed roller pairs arranged one behind the other. Crop which comes from a harvesting attachment of the harvester is drawn between the rollers and further transported for example to a chopping drum or another working aggregate. The metal detecting device is located conventionally stationarily inside one of the front feed rollers. The detection region of the metal detecting device is formed by a measuring magnet field produced the magnetic arrangement. The measuring magnetic field is oriented preferably substantially vertically from below into the crop stream or often also inclinedly forwardly in direction of the harvesting attachment. The measuring magnetic field is selected with its intensity so that it penetrates at least a greater part of the crop layer. The magnet arrangement is composed mainly of a plurality of permanent magnets arranged transversely to the product flow direction.
When a metal part which is a ferromagnetic interfering element, reaches this detection region, the magnetic field is partially increased. This magnetic field change is registered by the sensing device. The sensing device conventionally has a plurality of sensor elements. As a rule, they are coils, in which a signal is induced in response to the change of the measuring magnetic field. Basically, also other magnetic field sensors, for example Hall sensors can be used as well. The signal outputted from the sensor device is supplied to a signal evaluation device which evaluates the signal to determine whether the magnetic field change was caused by a metal part in the product to be supplied. In the evaluating circuit the signal for example is amplified, and in some cases digitalized, filtered and set with a threshold value.
When the set threshold value is exceeded, an output signal is for example generated, which then is supplied to a fast stopping device for the whole machine or for the feeding aggregate, for example on the conveyor. Then in a very short time, before the metal part can reach a working aggregate located after the conveyor, for example in a forage harvester it is a chopping drum, the machine or the conveyor is stopped. When the machine is stopped, the operator of the conveyor must activate a throwing-out device and the crop is again thrown out and searched to remove the metal part. Thereby the damages for the subsequent working aggregates as well as a contamination of the crop by metal parts are efficiently prevented.
The mounting position of the metal detecting device causes however disturbances which can lead to a sfaulty release of the metal detection device. The metal detector is arranged inside the feeding roller protected from damages and wear, the however movable parts are located in the detection region which can lead to a change of the detection condition and to a faulty triggering. For example the outer surface of the feed roller is profiled and influences the magnetic field. Furthermore, for example the upper roller of the feed rollers is supported vertically movable and adapts its distance from the lower feed roller to the crop throughput. These movements also can lead to influencing the magnetic field. For reducing the structurally-dependent influences, non-ferromagnetic materials can be used in the detection region and the neighboring regions, such as VA steels or synthetic plastics. An example for this solution is disclosed in the German patent document DE 199 12 407 A1. Other influences which can lead to a faulty triggering of the metal detecting device include an external magnetic field, for example the earth magnetic field or magnetic fields of electric current cables laid in the ground.
When the harvesting operation is interrupted frequently by faulty triggering, this leads to increase of harvesting cost. In addition, correspondingly a correct triggering is faster recognized by operator erroneously as a faulty triggering and can lead to a new activation of the feeding without searching of the crop, that can lead to damages of the working aggregates. Excessively frequent fault triggerings finally lead to a decrease of reliability of the metal detecting device. The number of the faulty triggering can be reduced by an intelligent signal evaluation with signal filtering and so-called response-threshold. When however the response threshold of the metal detector is set very high to avoid a faulty triggering, there is a danger that metal parts are caught in the machine undetected. In particular, small metal parts which travel through the whole machine unobjectionably are not detected and contaminate the crop. Furthermore, the adjustment of the response threshold of the signal evaluation device of the metal detector represents always a compromise between possible faulty triggerings and possible damages to the machine or a contamination of the crop by non-detected metal parts.